Intra- and inter-rater reliability for transvaginal cervical strain elastography

Cervical strain elastography has been explored as a biomarker for preterm birth but is limited by poor reliability due to difficulty standardizing the external compression. E-Cervix™ has been proposed to address this limitation by utilizing intrinsic maternal arterial pulsations as the vibration force, rather than an external force. However, given the novel nature of this proprietary technique, we sought to assess the measurement reliability in our clinical setting. Experienced MFM sonographers were trained on Samsung Hera-W10 machines using the vendor-supplied E-Cervix™ protocol until they produced 10 acceptable elastograms. For each subject, 2 sonographers each performed 3 acquisitions and measurements. All scans were performed during clinically indicated transvaginal exams on consented subjects. A two-way mixed effects model evaluated intra-rater single measure agreement and inter-rater average measure agreement. An intraclass correlation (ICC) >0.75 indicates acceptable reliability. After a vendor update to improve E-Cervix™ software, we repeated the study with the same sonographers to determine if reliability was affected. Finally, we analyzed cervical length (CL), acquired at the same time as elastography, to serve as a reference source of variability. The primary analysis included (n1= 43) subjects each scanned by 2 sonographers. Of the 5 elastographic parameters, only the ratio of internal to external os strain had an intra-rater ICC >0.75 in the initial cohort. No parameter had an acceptable inter-rater ICC. Similarly, no elastogram parameter had adequate intra- or inter-rater ICC in the post-update group (n2 =13 subjects). CL on the other hand, maintained excellent reliability in both phases. Despite more favorable results in the literature, strain elastography with E-Cervix™ did not demonstrate adequate reliability in our study. Given the numerous variables that may impact intrinsic pelvic vibrations, it is critical for each center to confirm reliability of novel quantitative techniques prior to conducting prospective investigation.View Large Image Figure ViewerDownload Hi-res image Download (PPT)